U.S. patent number 10,938,050 [Application Number 15/818,662] was granted by the patent office on 2021-03-02 for membrane electrode assembly for fuel cells and manufacturing method thereof.
This patent grant is currently assigned to Hyundai Motor Company, Kia Motors Corporation. The grantee listed for this patent is HYUNDAI MOTOR COMPANY, KIA MOTORS CORPORATION. Invention is credited to Bo Ki Hong, Jong Kil Oh.
United States Patent |
10,938,050 |
Oh , et al. |
March 2, 2021 |
Membrane electrode assembly for fuel cells and manufacturing method
thereof
Abstract
A membrane electrode assembly includes: an electrolyte membrane;
a cathode and an anode, each being stacked on the electrolyte
membrane; and subgaskets bonded to a peripheral region of the
electrolyte membrane, which is outside an active area, in which
each of the cathode and the anode are stacked on the electrolyte
membrane. The electrolyte membrane is disposed in at least a
portion of the peripheral region of the electrolyte membrane, which
is outside the active area, with a water discharge blocking region
for preventing water in the electrolyte membrane from diffusing and
being discharged to outside.
Inventors: |
Oh; Jong Kil (Yongin-si,
KR), Hong; Bo Ki (Seoul, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
HYUNDAI MOTOR COMPANY
KIA MOTORS CORPORATION |
Seoul
Seoul |
N/A
N/A |
KR
KR |
|
|
Assignee: |
Hyundai Motor Company (Seoul,
KR)
Kia Motors Corporation (Seoul, KR)
|
Family
ID: |
1000005396328 |
Appl.
No.: |
15/818,662 |
Filed: |
November 20, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20180166721 A1 |
Jun 14, 2018 |
|
Foreign Application Priority Data
|
|
|
|
|
Dec 13, 2016 [KR] |
|
|
10-2016-0169485 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M
8/1004 (20130101); H01M 8/1041 (20130101); H01M
8/1065 (20130101); H01M 8/0273 (20130101); H01M
8/04119 (20130101); H01M 8/0271 (20130101); H01M
8/1016 (20130101); H01M 8/1088 (20130101); Y02P
70/50 (20151101) |
Current International
Class: |
H01M
8/1004 (20160101); H01M 8/1041 (20160101); H01M
8/1088 (20160101); H01M 8/04119 (20160101); H01M
8/1016 (20160101); H01M 8/0273 (20160101); H01M
8/0271 (20160101); H01M 8/1065 (20160101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
K Hongsirikam et al., "Effect of cations (Na+, Ca2+, Fe3+) on the
conductivity of a Nafion membranne," Journal of Power Sources 195
(2010) pp. 7213-7220. cited by applicant .
M.J. Kelly et al., "Contaminant absorption and conductivity in
polymer electrolyte membranes," Journal of Power Sources, 145
(2005), pp. 249-252. cited by applicant .
D.A. Shores et al., "Basic material corrosion issues," Handbook of
Fuel Cells--Fundamentals, Technology and Application, (2010) pp.
1-13. cited by applicant.
|
Primary Examiner: Lee; James
Attorney, Agent or Firm: Morgan, Lewis & Bockius LLP
Claims
What is claimed is:
1. A membrane electrode assembly for fuel cells comprising: an
electrolyte membrane; a cathode and an anode, each being stacked on
the electrolyte membrane; and subgaskets bonded to a peripheral
region of the electrolyte membrane, which is outside an active
area, in which each of the cathode and the anode are stacked on the
electrolyte membrane, wherein the peripheral region of the
electrolyte membrane is outside the active area and includes a
first peripheral region and a second peripheral region, the second
peripheral region being outside the first peripheral region and
including a water discharge blocking region for preventing water in
the electrolyte membrane from diffusing and being discharged to
outside, and wherein the water discharge blocking region is formed
by metal cation substitution.
2. The membrane electrode assembly of claim 1, wherein the water
discharge blocking region is formed in a portion of the peripheral
region of the electrolyte membrane that is spaced apart from the
active area.
3. The membrane electrode assembly of claim 1, wherein the water
discharge blocking region extends along sides of the electrolyte
membrane at the peripheral region of the electrolyte membrane to
have a predetermined width.
4. The membrane electrode assembly of claim 1, wherein the
subgaskets are stacked on the entire peripheral region of the
electrolyte membrane excluding the active area, in which each of
the cathode and the anode are stacked on the electrolyte
membrane.
5. The membrane electrode assembly of claim 1, wherein the water
discharge blocking region is formed in the peripheral region of the
electrolyte membrane along four sides of the electrolyte
membrane.
6. The membrane electrode assembly of claim 1, wherein the water
discharge blocking region is formed in the peripheral region of the
electrolyte membrane along two opposite sides of the electrolyte
membrane, among four sides of the electrolyte membrane.
7. The membrane electrode assembly of claim 1, wherein the water
discharge blocking region is formed in a portion of the peripheral
region of the electrolyte membrane, which is spaced apart from the
active area along sides of the electrolyte membrane, and has a
predetermined width, and wherein a width of the water discharge
blocking region is 0.5 times or less a total width of the
peripheral region of the electrolyte membrane.
8. The membrane electrode assembly of claim 1, wherein the water
discharge blocking region is formed as a result of protons coupled
in a sulfonic acid group (-SO.sub.3.sup.-H.sup.+) of the
electrolyte membrane being substituted by metal cations.
9. The membrane electrode assembly of claim 8, wherein the metal
cations are selected from the group consisting of Na, Li, K, Ca,
Mg, Cu, Zn, Ni, Fe, Cr, and Ai.
10. The membrane electrode assembly of claim 8, wherein the metal
cations are bivalent or trivalent metal cations.
11. The membrane electrode assembly of claim 1, wherein the water
discharge blocking region is disposed on the peripheral region of
the electrolyte membrane in a lateral direction perpendicular to a
stacking direction of the anode and the cathode on the electrolyte
membrane.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application claims under 35 U.S.C. .sctn. 119(a) the benefit
of priority to Korean Patent Application No. 10-2016-0169485 filed
on Dec. 13, 2016, the entire content of which is incorporated
herein by reference.
TECHNICAL FIELD
The present disclosure relates to a membrane electrode assembly for
fuel cells and a manufacturing method thereof. More particularly,
the present disclosure relates to a membrane electrode assembly for
fuel cells capable of preventing water in an electrolyte membrane
of the membrane electrode assembly from diffusing to a peripheral
region of the electrolyte membrane, which is outside an active area
of a fuel cell, thereby preventing loss of the water used for fuel
cell reaction in the electrolyte membrane, to improve efficiency in
handling of water in the fuel cell, and to improve corrosion
resistance of a stack and a manufacturing method thereof.
BACKGROUND
A fuel cell is a power generation device that induces an
electrochemical reaction between fuel gas and oxidizing gas to
convert chemical energy in fuel into electrical energy. Such a fuel
cell is widely used for a power source in industries, homes, and
vehicles. The fuel cell may also be used to supply power to
small-sized electric/electronic products or portable devices.
To date, a polymer electrolyte membrane fuel cell (PEMFC), which
exhibits high power density, has been widely used as the fuel cell
for vehicles. The polymer electrolyte membrane fuel cell is used as
a power source for supplying power to a motor for driving a fuel
cell vehicle and various kinds of electric devices of the fuel cell
vehicle.
In the polymer electrolyte membrane fuel cell, hydrogen is used as
fuel gas, and oxygen or air including oxygen is used as oxidizing
gas.
In addition, the fuel cell includes a cell in which the fuel gas
and the oxidizing gas react with each other to generate electrical
energy. In general, a plurality of cells is stacked and connected
to each other in series in the form of a stack to satisfy power
requirements.
The fuel cell for vehicles requires high power. For this reason,
several hundred unit cells, each of which generates electrical
energy, are stacked in the form of a stack.
Each unit cell of the polymer electrolyte membrane fuel cell
includes a membrane electrode assembly (MEA), which includes a
polymer electrolyte membrane capable of moving protons and
electrodes attached to opposite surfaces of the polymer electrolyte
membrane, a gas diffusion layer (GDL) for supplying reaction gases,
such as fuel gas and oxidizing gas, to the membrane electrode
assembly and transmitting generated electrical energy, a gasket for
maintaining airtightness of the reaction gases and coolant, a
fastening member for maintaining appropriate fastening pressure,
and a bipolar plate (BP) for moving the reaction gases and the
coolant.
The membrane electrode assembly (MEA) includes a polymer
electrolyte membrane capable of moving protons and an anode and a
cathode attached to opposite surfaces of the polymer electrolyte
membrane, a catalyst for inducing a reaction between hydrogen,
which is fuel gas, and air (or oxygen), which is oxidizing gas,
being applied to the anode and the cathode.
A gas diffusion layer (GDL) for uniformly distributing the fuel gas
and the oxidizing gas is stacked on the outside of the membrane
electrode assembly, i.e. the outside of each of the anode and the
cathode, and a bipolar plate for providing a channel, along which
reaction gases and coolant flow, and supplying the reaction gases
to the gas diffusion layer is disposed at the outside of the gas
diffusion layer.
In addition, a gasket for fluid sealing is disposed between parts
constituting unit cells. The gasket may be integrally formed with
the membrane electrode assembly or the bipolar plate.
The above elements constitute a unit cell. A plurality of cells is
stacked, end plates for supporting the cells are coupled to the
outermost ends of the stacked cells, and the end plates are
fastened to the cells using a stack fastening member to constitute
a fuel cell stack.
A reaction in the fuel cell for generating electrical energy is
performed in a membrane electrode assembly (MEA) including a
perfluorinated sulfonic acid (PFSA) electrolyte membrane and
electrodes, such as an anode and a cathode.
At this time, fuel gas, i.e. hydrogen, supplied to the anode, which
is an oxidation electrode (i.e. a fuel electrode) of the fuel cell,
is separated into protons and electrons. The protons move to the
cathode, which is a reduction electrode (i.e. an air electrode)
through the electrolyte membrane. Oxygen molecules, protons, and
electrons react together at the cathode, with the result that
electricity and heat are generated. At the same time, water is
generated as a reaction by-product.
In particular, when the protons move from the anode to the cathode
through the membrane, the protons are coupled to water molecules in
the form of hydronium ions, with the result that an electro-osmotic
drag (EOD) phenomenon, in which the protons drag the water
molecules, occurs.
In addition, if the amount of water accumulated in the cathode
increases, a back diffusion phenomenon, in which some of the water
moves backward from the cathode to the anode, may occur.
If the amount of water that is generated by the fuel cell reaction
and is then moved is appropriate, it is possible to maintain the
wettability of the membrane electrode assembly (MEA). However, if
the amount of water is excessive, a water flooding phenomenon
occurs. For this reason, it is necessary to appropriately remove
the excessive amount of water.
In addition, the flooded water prevents reaction gases from being
efficiently supplied into the unit cells of the fuel cell, whereby
voltage loss is further increased.
In order to enable the fuel cell to stably operate within a wide
current density range, and therefore, it is necessary to accurately
understand such a water movement phenomenon and to efficiently use
the water in the fuel cell.
In general, compression pressure, generated by the gasket, which is
made of a rubber elastomer, is applied to the membrane electrode
assembly for a long time. The shape of the membrane electrode
assembly must be maintained without being tom or deformed even when
the membrane electrode assembly is compressed for a long time.
In addition, high stiffness is required in order to improve a
handling property during stacking of membrane electrode
assemblies.
For this reason, a solid-phase, film-shaped subgasket exhibiting
high stiffness is laminated to a peripheral region of the membrane
by applying heat.
If the membrane electrode assembly includes such a subgasket,
membrane electrode assemblies may be used for a long time even when
several hundred membrane electrode assemblies are stacked in one
stack.
In the structure of a conventional membrane electrode assembly, an
electrolyte membrane is manufactured such that, in addition to an
active area, in which a cathode and an anode, which are used to
induce an electrochemical reaction in the fuel cell, are bonded to
the electrolyte membrane, an extended region is formed outside the
active area of the fuel cell in order to securely bond the
subgasket to the electrolyte membrane. The subgasket is bonded to
the extended region, i.e. a peripheral region, of the electrolyte
membrane.
In the structure of the conventional membrane electrode assembly,
however, water may diffuse to the peripheral region of the
electrolyte membrane, to which the subgasket is bonded, which is
not desirable. As a result, the water used for the fuel cell
reaction may be lost.
In addition, the diffused water may corrode the other parts of the
stack that are made of metal materials, whereby the stability in
travel of the vehicle may be greatly lowered.
In order to solve the above problems, there has been proposed a
method of reducing the size of the peripheral region of the
electrolyte membrane, which is outside the active area of the
membrane electrode assembly (MEA), i.e. the peripheral region of
the electrolyte membrane, to which the subgasket is bonded, so as
to be less than the size of the subgasket, thereby preventing the
membrane of the membrane electrode assembly from being exposed to
the outside and thus preventing water from being discharged to the
outside.
However, the reaction gases and the coolant may leak due to the
step between the region of the subgasket to which the electrolyte
membrane is bonded and the region of the subgasket to which the
electrolyte membrane is not bonded. Furthermore, the membrane and
the subgasket may be separated from each other after operation of
the fuel cell for a long time, with the result that the operation
of the fuel cell may be stopped.
Alternatively, methods of bonding the subgasket to the membrane
electrode assembly through injection molding rather than lamination
have been proposed. When the subgasket is injection-molded using
these methods, the membrane electrode assembly may be deformed or
contaminated.
In addition, a complicated multistage process may be performed in
order to solve the above problems. As a result, a subgasket bonding
process is complicated, whereby productivity is reduced.
SUMMARY OF THE DISCLOSURE
The present disclosure has been made in an effort to solve the
above-described problems associated with the related art. Thus the
present disclosure is directed to providing a membrane electrode
assembly for fuel cells configured such that it is possible to
prevent water in an electrolyte membrane of the membrane electrode
assembly from diffusing to a peripheral region of the electrolyte
membrane, which is outside an active area of a fuel cell, thereby
preventing the loss of the water used for fuel cell reaction in the
electrolyte membrane, to improve efficiency in handling of water in
the fuel cell, and to improve corrosion resistance of a stack and a
manufacturing method thereof.
According to an exemplary embodiment of the present disclosure, a
membrane electrode assembly for fuel cells includes: an electrolyte
membrane; a cathode and an anode, each being stacked on the
electrolyte membrane; and subgaskets bonded to a peripheral region
of the electrolyte membrane, which is outside an active area, in
which the cathode and the anode are stacked on the electrolyte
membrane. The electrolyte membrane is provided in at least a
portion of the peripheral region of the electrolyte membrane, which
is outside the active area, with a water discharge blocking region
for preventing water in the electrolyte membrane from diffusing and
being discharged to the outside.
According to another exemplary embodiment of the present
disclosure, a method of manufacturing a membrane electrode assembly
for fuel cells includes: applying a metal cation solution, having a
metal cation precursor dissolved in a solvent, to at least a
selected portion of a peripheral region of an electrolyte membrane,
which is outside an active area of the electrolyte membrane, in
which a cathode and an anode are stacked on the electrolyte
membrane, to form a water discharge blocking region; stacking the
cathode and the anode on the active area of the electrolyte
membrane; and stacking subgaskets on the peripheral region of the
electrolyte membrane, which is outside the active area, in which
the cathode and the anode are stacked on the electrolyte membrane.
The water discharge blocking region is formed as a result of
protons coupled in a sulfonic acid group (--SO.sub.3.sup.-H.sup.+)
of the electrolyte membrane being substituted by metal cations in
the solution.
Other aspects and embodiments of the disclosure are discussed
infra.
It is understood that the term "vehicle" or "vehicular" or other
similar term as used herein is inclusive of motor vehicles in
general such as passenger automobiles including sports utility
vehicles (SUV), buses, trucks, various commercial vehicles,
watercraft including a variety of boats and ships, aircraft, and
the like, and includes hybrid vehicles, electric vehicles, plug-in
hybrid electric vehicles, hydrogen-powered vehicles and other
alternative fuel vehicles (e.g. fuels derived from resources other
than petroleum). As referred to herein, a hybrid vehicle is a
vehicle that has two or more sources of power, for example both
gasoline-powered and electric-powered vehicles.
The above and other features of the disclosure are discussed
infra.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features of the present disclosure will now be
described in detail with reference to certain exemplary embodiments
thereof illustrated in the accompanying drawings which are given
hereinbelow by way of illustration only, and thus are not
limitative of the present disclosure, and wherein:
FIG. 1 shows a membrane electrode assembly according to an
embodiment of the present disclosure;
FIG. 2 shows a membrane electrode assembly according to another
embodiment of the present disclosure; and
FIG. 3 shows a membrane electrode assembly according to a further
embodiment of the present disclosure.
It should be understood that the appended drawings are not
necessarily to scale, presenting a somewhat simplified
representation of various features illustrative of the basic
principles of the disclosure. The specific design features of the
present disclosure as disclosed herein, including, for example,
specific dimensions, orientations, locations, and shapes, will be
determined in part by the particular intended application and use
environment.
In the figures, reference numbers refer to the same or equivalent
parts of the present disclosure throughout the several figures of
the drawing.
DETAILED DESCRIPTION
Hereinafter, the exemplary embodiment of the present disclosure
will be described in detail with reference to the accompanying
drawings to allow those skilled in the art to easily practice the
present disclosure.
Advantages and features of the present disclosure and methods for
achieving the same will be clearly understood with reference to the
following detailed description of embodiments in conjunction with
the accompanying drawings.
However, the present disclosure is not limited to the embodiments
disclosed herein, but may be implemented in various different
forms. The embodiments are merely given to make the disclosure of
the present disclosure perfect and to perfectly instruct the scope
of the disclosure to those skilled in the art, and the present
disclosure should be defined by the scope of claims.
In addition, in the description of the present disclosure, a
detailed description of related known technologies and the like
will be omitted when it makes the subject of the present disclosure
unclear.
The terms "comprises" and "comprising" described herein should be
interpreted not to exclude other elements but to further include
such other elements unless mentioned otherwise.
The present disclosure provides a membrane electrode assembly for
fuel cells configured such that it is possible to prevent water in
an electrolyte membrane of the membrane electrode assembly from
diffusing to a peripheral region of the electrolyte membrane, which
is outside an active area of a fuel cell without reduction of fuel
cell operation performance and damage to airtightness, thereby
preventing the loss of the water used for fuel cell reaction in the
electrolyte membrane, to improve efficiency in handling of water in
the fuel cell, and to improve corrosion resistance of a stack and a
manufacturing method thereof.
FIG. 1 is a plan view and sectional views showing a membrane
electrode assembly according to an embodiment of the present
disclosure.
As shown in FIG. 1, a membrane electrode assembly (MEA) 10
according to the present disclosure, which is used in a polymer
electrolyte membrane fuel cell (PEMFC), includes a polymer
electrolyte membrane 11 capable of moving protons, an anode 13 and
a cathode 12 attached to opposite surfaces of the polymer
electrolyte membrane 11, a catalyst for inducing a reaction between
hydrogen, which is fuel gas, and air (or oxygen), which is
oxidizing gas, being applied to the anode 13 and the cathode 12,
and subgaskets 14 bonded to opposite surfaces of a peripheral
region of the polymer electrolyte membrane 11.
The membrane electrode assembly 10 has an area in which the anode
13 and the cathode 12 are bonded to the polymer electrolyte
membrane 11, which is an area in which an electrochemical reaction
occurs, i.e. an active area, to which the fuel gas and the
oxidizing gas are supplied such that a reaction occurs in a fuel
cell.
That is, the cathode 12 and the anode 13 are attached to opposite
surfaces of the membrane electrode assembly 10, and the area in
which the cathode 12 and the anode 13 are bonded to the polymer
electrolyte membrane 11 is an active area, in which reaction occurs
in the fuel cell.
In addition, the subgaskets 14 are bonded to the peripheral region
of the polymer electrolyte membrane 11 excluding the active area,
in which the cathode 12 and the anode 13 are bonded to the polymer
electrolyte membrane 11. The subgaskets 14 may be bonded to the
entire peripheral region of the polymer electrolyte membrane 11
excluding the active area.
FIG. 1 is a plan view of the membrane electrode assembly. In
addition, FIG. 1 is a sectional view taken along line X-X of the
plan view and a sectional view taken along line Y-Y of the plan
view. Here, line X-X may be a line extending in a longitudinal
direction of the membrane electrode assembly 10 while passing
through the active area, and line Y-Y may a line extending in the
lateral direction of the membrane electrode assembly 10 while
passing through the active area.
Referring to FIG. 1, the active area of the membrane electrode
assembly 10, in which the cathode 12 and the anode 13 are bonded to
the polymer electrolyte membrane 11, is located in the middle of
the membrane electrode assembly in a rectangular shape.
In addition, the subgaskets 14 are bonded to the peripheral region
of the polymer electrolyte membrane 11 excluding the middle active
area, in which the cathode 12 and the anode 13 are bonded to the
polymer electrolyte membrane 11. Each subgasket 14 has a
rectangular opening formed in the middle thereof such that the
middle active area is exposed through the opening, i.e. such that
the cathode 12 and the anode 13 are exposed, through the
opening.
More specifically, each subgasket 14 is formed in a rectangular
frame shape such that each subgasket 14 is located at the
rectangular edge of the membrane electrode assembly 10. At this
time, the subgaskets 14 may be stacked and bonded to the opposite
surfaces of the polymer electrolyte membrane 11 at the peripheral
region of the polymer electrolyte membrane 11, which is outside the
cathode 12 and the anode 13 (i.e. the active area) such that the
subgaskets 14 do not overlap the cathode 12 or the anode 13.
Meanwhile, the membrane electrode assembly 10 according to the
present disclosure further includes a water discharge blocking
region 11a formed in at least a portion of the peripheral region of
the polymer electrolyte membrane 11, to which the subgaskets 14 are
bonded.
The water discharge blocking region 11a is configured to prevent
water in the polymer electrolyte membrane 11 from moving to the
peripheral region of the polymer electrolyte membrane 11, which is
outside the active area, due to diffusion thereof. That is, the
water discharge blocking region 11a prevents water used for
reaction in the fuel cell from diffusing to the peripheral region
of the polymer electrolyte membrane 11 and being discharged out of
the fuel cell, thereby preventing the water from being lost.
By the provision of the water discharge blocking region 11a, it is
possible to prevent the movement and diffusion of water to the
peripheral region of the polymer electrolyte membrane 11 and the
discharge of the water to the outside, thereby preventing loss of
the water. Consequently, it is possible to prevent a stack from
being corroded by water discharged from each cell, thereby
improving the corrosion resistance of the stack. In addition, it is
possible to improve efficiency in handling of water in the fuel
cell.
According to the present disclosure, the water discharge blocking
region 11a is formed in the peripheral region of the polymer
electrolyte membrane 11, to which the subgaskets 14 are bonded, by
additional processing. After the processing, the peripheral region
of the polymer electrolyte membrane 11 may perform a water
discharge blocking function.
In addition, the water discharge blocking region 11a may extend
along sides of the polymer electrolyte membrane 11 at the
peripheral region of the polymer electrolyte membrane 11 so as to
have a predetermined width. As illustrated in FIG. 1, the water
discharge blocking region 11a may extend along the entire
peripheral region of the polymer electrolyte membrane 11 so as to
have a rectangular frame shape.
That is, as shown in FIG. 1, on the assumption that the peripheral
region of the polymer electrolyte membrane 11, to which the
subgaskets 14 are bonded, is formed in a rectangular frame shape,
the water discharge blocking region 11a is formed in a portion of
the peripheral region of the polymer electrolyte membrane 11 that
is spaced apart from the active area by a predetermined distance so
as to have a predetermined width.
Since the water discharge blocking region 11a is formed in the
peripheral region of the polymer electrolyte membrane 11, to which
the subgaskets 14 are bonded, the subgaskets 14 are stacked and
bonded to the water discharge blocking region 11a of the polymer
electrolyte membrane 11.
As shown in FIG. 1, the water discharge blocking region 11a is
formed in the polymer electrolyte membrane 11 along four sides of
the membrane electrode assembly 10, i.e. two long sides and two
short sides thereof, so as to have a predetermined width at each
side. The water discharge blocking region 11a is formed in a
rectangular frame shape.
The width of the water discharge blocking region 11a of the polymer
electrolyte membrane 11 may be 0.5 times or less the total width of
the peripheral region of the polymer electrolyte membrane 11.
In short, the water discharge blocking region 11a of the polymer
electrolyte membrane 11 is formed in a portion of the peripheral
region of the polymer electrolyte membrane 11 excluding the active
area (i.e. the electrochemical reaction area), in which the cathode
12 and the anode 13 are bonded to the polymer electrolyte membrane
11, i.e. the region in which the subgaskets are bonded to the
polymer electrolyte membrane 11, spaced apart from the active area
by a predetermined distance set at each side. At this time, the
width of the water discharge blocking region 11a at an arbitrary
position of each side may be 0.5 times or less the total width of
the region in which the subgaskets are bonded to the polymer
electrolyte membrane 11 at the same position.
If the width of the water discharge blocking region 11a is greater
than 0.5 times the total width of the region in which the
subgaskets are bonded to the polymer electrolyte membrane 11, the
water discharge blocking region 11a, which is formed by metal
cation substitution, as will be described below, is too close to
the active area (i.e. the electrochemical reaction area), with the
result that electrochemical reaction (i.e. fuel cell reaction) may
be affected.
Unlike the embodiment of FIG. 1, the water discharge blocking
region 11a may be formed in a portion of the peripheral region of
the polymer electrolyte membrane 11, more specifically, only two
opposite sides of the polymer electrolyte membrane 11, among the
four sides of the polymer electrolyte membrane 11.
FIGS. 2 and 3 show embodiments in which the water discharge
blocking region 11a is formed in only two opposing sides of the
polymer electrolyte membrane 11. FIG. 2 shows an embodiment in
which the water discharge blocking region 11a is formed in only two
opposing long sides of the polymer electrolyte membrane 11, among
the four sides of the polymer electrolyte membrane 11. FIG. 3 shows
an embodiment in which the water discharge blocking region 11a is
formed in only two opposing short sides of the polymer electrolyte
membrane 11, among the four sides of the polymer electrolyte
membrane 11.
In each embodiment, the water discharge blocking region 11a may be
spaced apart from the active area by a predetermined distance at
each side, as described above. Even in the embodiments of FIGS. 2
and 3, the width of the water discharge blocking region 11a at an
arbitrary position of each side may be 0.5 times or less the total
width of the region in which the subgaskets are bonded to the
polymer electrolyte membrane 11 at the same position.
That is, in embodiments of FIGS. 1 to 3, the width of the water
discharge blocking region 11a at an arbitrary position of each side
may be less than the distance from the active area.
The reasons for this are that the water discharge blocking region
11a is spaced apart from the active area, in which the cathode 12
and the anode 13 are bonded to the polymer electrolyte membrane 11
and that the peripheral region of the polymer electrolyte membrane
11 (i.e. the region in which the subgaskets 14 are bonded to the
polymer electrolyte membrane 11) outside the active area of the
polymer electrolyte membrane 11 is divided into a portion forming
the water discharge blocking region 11a and a portion forming only
the polymer electrolyte membrane 11.
According to an embodiment of the present disclosure, the water
discharge blocking region 11a may be formed by applying a solution
containing metal cations to the polymer electrolyte membrane 11
such that protons coupled in a sulfonic acid group
(--SO.sub.3.sup.-H.sup.+) of the polymer electrolyte membrane 11
are substituted by the metal cations.
That is, in the present disclosure, the water discharge blocking
region 11a for blocking the movement of water may be formed in the
polymer electrolyte membrane 11. The property of a portion of the
peripheral region of the polymer electrolyte membrane 11
corresponding to the water discharge blocking region 11a is changed
by selective cation substitution such that a specific region in the
polymer electrolyte membrane 11 forms the water discharge blocking
region 11a.
The water discharge blocking region 11a is realized by changing the
property of a portion of the region in which the subgaskets 14 are
bonded to the polymer electrolyte membrane 11 by cation
substitution. Consequently, the water discharge blocking region 11a
blocks the movement of water in the polymer electrolyte membrane 11
to the outside, whereby it is possible to prevent the water from
being discharged to the outside.
Prior research on the polymer electrolyte membrane shows that when
metal cations, such as Na.sup.+, Ca.sup.2+, and Fe.sup.3+, are
exposed to the membrane, ion conductivity is reduced and membrane
dehydration occurs (Kitiya Hongsirikam et al., J. Power Sources,
195, 7213-7220 (2010); Michael J. Kelly et al., J. Power Sources,
145, 249-252 (2005); D. A. Shores and G. A. Deluga, "Basic
materials corrosion issues", Ch. 23 in Handbook of Fuel
Cells--Fundamentals, Technology and Applications, Edited by Wolf
Vielstich, Hubert A. Gasteiger, Arnold Lamm., Volume 3, John Wiley
& Sons, Ltd. (2003)).
The reason for this is that protons coupled in a sulfonic acid
group (--SO.sub.3.sup.-H.sup.+) of the membrane are substituted by
cations, which exhibit higher affinity for a sulfonic group
(--SO.sub.3.sup.-) of the membrane than the protons, to disturb
coupling between the protons and water molecules.
In particular, multivalent cations, rather than monovalent cations,
are strongly affected.
If the above phenomenon occurs in the active area of the membrane
electrode assembly, ion conductivity is reduced, whereby the
performance of the fuel cell is greatly lowered.
However, in the case in which cation substitution is performed in
the peripheral region of the polymer electrolyte membrane 11
outside the active area, i.e. the region in which the subgaskets 14
are bonded to the polymer electrolyte membrane 11, the water
content of the membrane may be reduced without affecting the fuel
cell reaction, thereby greatly reducing the amount of water
discharged out of the membrane electrode assembly.
In the present disclosure, therefore, the polymer electrolyte
membrane 11 includes a water discharge blocking region 11a formed
in the peripheral region of the polymer electrolyte membrane 11
outside the active area by selective cation substitution.
The water discharge blocking region 11a in the polymer electrolyte
membrane 11 is formed in at least a portion of the outer part of
the region in which the subgaskets 14 are bonded to the polymer
electrolyte membrane 11, excluding the active area, which is an
electrochemical reaction part.
Hereinafter, a process of forming the water discharge blocking
region in the polymer electrolyte membrane will be described.
First, as a method of forming the water discharge blocking region
11a in a selected region of the polymer electrolyte membrane 11,
opposite surfaces of the polymer electrolyte membrane 11, excluding
the water discharge blocking region 11a, are covered with a masking
member (not shown), and a metal cation solution having a metal
cation precursor dissolved in a solvent is applied to the exposed
region of the polymer electrolyte membrane 11, which is not covered
by the masking member, through a wet process, such as spraying,
brushing, or rolling.
Alternatively, the water discharge blocking region may be
simultaneously formed in the peripheral region of the polymer
electrolyte membrane outside the active area of the cell by
spraying a metal cation solution to the side surfaces of a fuel
cell stack after assembling the fuel cell stack. However, the
present disclosure is not limited thereto.
In the present disclosure, the metal (M) cation solution may
include a metal cation precursor represented by [Chemical Formula
1] below and a solvent. M(X)n [Chemical Formula 1]
Where M may be selected from a group consisting of Na, Li, K, Ca,
Mg, Cu, Zn, Ni, Fe, Cr, and Al, and X may be selected from a group
consisting of chloride, sulfate, acetate, nitrate, hydroxide, and a
combination thereof.
In addition, n is set based on the valence of M.
In the present disclosure, the metal cation solution may include
one or more metal cation precursors. The metal cations, generated
from the metal (M), may be bivalent metal cations. More
specifically, the metal cations may be bivalent or trivalent metal
cations.
In addition, the concentration of the metal cations in the solution
may be at least 1 mol %. If the concentration of the metal cations
is less than 1 mol %, cation substitution is not sufficiently
performed, with the result that water discharge blocking efficiency
may be reduced.
The solvent is used to dissolve the metal cation precursor. One or
a mixture of two or more selected from a group consisting of
de-ionized water, methanol, ethanol, iso-propyl alcohol,
1-propanol, and 2-methoxyethanol may be used as the solvent.
De-ionized water may be used.
After the metal cation solution is applied to a selected region of
the polymer electrolyte membrane 11 to form the water discharge
blocking region 11a, as described above, the polymer electrolyte
membrane 11 is dried and the masking member is removed for a time
sufficient to perform cation substitution.
The polymer electrolyte membrane 11 may be dried using a natural
drying method. Alternatively, a hot air drying method or a vacuum
drying method may be used in order to reduce drying time.
After the masking member is removed to obtain the polymer
electrolyte membrane 11, the cathode 12 and the anode 13 are
stacked on the polymer electrolyte membrane 11, and the subgaskets
14 are stacked and bonded to the polymer electrolyte membrane 11
using an ordinary process.
After the cathode 12 and the anode 13 are formed, the water
discharge blocking region 11a may be formed.
As a result, the water discharge blocking region, which is formed
by metal cation substitution, is formed in the peripheral region of
the polymer electrolyte membrane, which is outside the active area
of the membrane electrode assembly, whereby it is possible to
achieve an excellent handling property owing to the subgaskets,
which is required of the membrane electrode assembly, to maintain
the airtightness of the fuel cell, and to prevent the diffusion of
water to the peripheral region of the fuel cell through the use of
the water discharge blocking region.
Consequently, it is possible to improve efficiency in handling of
water in the fuel cell, to improve corrosion resistance of the
stack, and to improve safety in travel of a vehicle.
In FIGS. 1 to 3, A' and A'' indicate the electrochemical reaction
part, i.e. the active area of the membrane electrode assembly, in
which the cathode 12 and the anode 13 are bonded to the polymer
electrolyte membrane 11, and B' and B'' indicate the region in
which the subgaskets 14 are bonded to the polymer electrolyte
membrane 11, i.e. the peripheral region of the polymer electrolyte
membrane 11, which is outside the active area.
More specifically, A' indicates the length of the active area, and
A'' indicates the width of the active area.
In addition, B' indicates the width of the peripheral region at
each short side, and B'' indicates the width of the peripheral
region at each long side.
In addition, B1' and B1'' indicate a portion of the peripheral
region of the polymer electrolyte membrane 11 in which cation
substitution has not been performed, i.e. a cation un-substitution
region, which is provided to separate the active area of the
polymer electrolyte membrane 11 and the water discharge blocking
region 11a from each other.
B1' indicates the width of the cation un-substitution region at
each short side (i.e. the distance between the active area the
water discharge blocking region), and B1'' indicates the width of
the cation un-substitution region at each long side (i.e. the
distance between the active area the water discharge blocking
region).
In addition, B2' and B2'' indicate the water discharge blocking
region 11a of the polymer electrolyte membrane 11, which is formed
by selective cation substitution. In the embodiment of FIG. 1, the
water discharge blocking region 11a is formed at four sides of the
polymer electrolyte membrane 11. In the embodiment of FIG. 2, the
water discharge blocking region 11a is formed at two opposing long
sides of the polymer electrolyte membrane 11. In the embodiment of
FIG. 3, the water discharge blocking region 11a is formed at two
opposing short sides of the polymer electrolyte membrane 11.
As described above, B2'.ltoreq.0.5.times.B' and
B2''.ltoreq.0.5.times.B'' are shown in the embodiment of FIG. 1,
and B2''.ltoreq.0.5.times.B'' is shown in the embodiment of FIG.
2.
In addition, B2'.ltoreq.0.5.times.B' is described in the embodiment
of FIG. 3.
As is apparent from the above description, in the membrane
electrode assembly for fuel cells according to the present
disclosure and the manufacturing method thereof, the water
discharge blocking region, which is formed by metal cation
substitution, is formed in the peripheral region of the polymer
electrolyte membrane, which is outside the active area of the
membrane electrode assembly, whereby it is possible to achieve an
excellent handling property due to the subgaskets, which is
required of the membrane electrode assembly, to maintain the
airtightness of the fuel cell, and to prevent the diffusion of
water to the peripheral region of the fuel cell through the use of
the water discharge blocking region.
Consequently, it is possible to improve efficiency in handling of
water in the fuel cell, to improve the corrosion resistance of the
stack, and to improve safety in travel of a vehicle.
The disclosure has been described in detail with reference to
embodiments thereof. However, it will be appreciated by those
skilled in the art that changes may be made in these embodiments
without departing from the principles and spirit of the disclosure,
the scope of which is defined in the appended claims and their
equivalents.
* * * * *